In recent years, resin products are used in extremely wide-ranging fields, and requirements for these resin products have also been diversified. As one of such requirements, light electrical appliance parts, various containers for foodstuffs and cosmetics, and many other plastic household utensils and the like are required to be provided with beautiful luster and patterns on their surfaces to enhance their product value without impairing the numerous characteristics inherent in resin products.
To meet this requirement, several thermoplastic resin compositions have hitherto been proposed which provide resin products the surface texture of which per se has pearl-like luster. For example, Japanese Patent Publication No. 31467/1971 discloses a resin composition consisting essentially of acrylic resin, saturated aliphatic olefin resin and styrene resin; Japanese Patent Publication No. 41905/1976 discloses a resin composition containing styrene resin, styrene-acrylic resin and styrene-butadiene block copolymer resin; and Japanese Patent Publication Nos. 161837/1980 and 5542/1980 (although the latter does not refer to pearl-like luster) discloses a resin composition containing styrene resin and olefin resin.
However, these resin products having pearl-like luster are still insufficient in kind and number, and cannot adequately meet the needs of the market. Also, even if beautiful pearl-like luster could be obtained, there have been such problems as deterioration in the properties of the resin products, including such mechanical strength as impact strength and hinging properties, as well as decrease in moldability. In addition, more than three kinds of resin must be compounded at a predetermined ratio, which results in higher production costs.
Hence, pearl-like pigments are in some cases used as a means of obtaining resin products having pearl-like luster, but the use of such pigments is not economical because of an increase in the number of molding processes, and it also has a defect that the pearl-like luster of the surface is susceptible to discoloration.
It is, therefore, an object of the present invention to provide a novel resin composition used in the manufacture of thermoplastic resin products having pearl-like luster.
It is another object of the present invention to provide novel thermoplastic resin moldings having pearl-like luster.
It is a still another object of the present invention to provide a method of manufacturing novel thermoplastic resin moldings having pearl-like luster.
It is a further object of the present invention to provide resin products having beautiful pearl-like patterns and luster and excellent mechanical strength such as impact strength and hinging properties by molding a thermoplastic resin composition containing a styrene-butadiene block copolymer having a specific block form and crystalline polypropylene.